A modern vehicle, such as a car, is provided with safety arrangements in order to prevent or avoid injury to a seat occupant of the vehicle in case of an accident. It is well-known to use a safety arrangement comprising a seat belt for restraining the movement of the seat occupant in case of a sudden change of speed of the vehicle. Yet, a modern seat belt permits the seat occupant to move during normal driving conditions or when the vehicle stands still by adjusting the used length of the seat belt according to the movements of the seat occupant, e.g., when the seat occupant leans forwards.
It is known to use a retractor to suddenly and forcefully retract the seat belt in case of a collision or imminent collision being detected, since it is beneficial for the seat occupant to be located close to a seat back and a headrest in such a situation. The sudden and forceful retraction of the seat belt may be uncomfortable for the seat occupant, and may even cause a minor injury to the seat occupant. However, the advantages of being seated close to the seat back and headrest in case of a collision outweigh any discomfort or minor injury.
It is also known to reposition a seat or a portion of the seat, e.g., the seat back, in order to bring the seat occupant into a more favorable position. Purely as an example, if the seat back is inclined backwards, it may be beneficial to move it to a more upright position, e.g., in case of a rear-end collision.
Document EP 2 743 142 A1 discloses a method for retracting a seat belt of a vehicle, the method comprising the steps of determining an excessive length LΔ of pulled out seat belt, the excessive length LΔ of pulled out seat belt being the difference between the current length L and the minimum length Lmin of pulled out seat belt, when the seat belt is in use, and in case of detecting a collision or and/or a risk situation involving the vehicle, retracting the seat belt by applying a refraction force F, the retraction force F being a function of the excessive length LΔ of pulled out seat belt.
According to document EP 2 743 142 A1, the length of pulled out seat belt is utilized for determining a magnitude of the retraction force. In an embodiment, it is shown that the retraction force may, at least partly, be increasing as a function of the excessive length LΔ of pulled out seat belt. This means that a higher force will be used if the seat occupant is far from the seat back, as compared to if the seat occupant is close to the seat back.